Various types of airbag devices have been employed for restraining an occupant's body upon collision of the automobile, for example, a driver-side airbag device which inflates and deploys the airbag from the rotating center of the steering wheel toward the driver in the driver's seat, or a passenger airbag which inflates and deploys from the instrument panel towards the passenger seat.
When the serious accident which exerts the large external force to the automobile occurs resulting from the overturn of the vehicle or the falling of the heavy load, for example, the fallen tree, the resultant impact may be exerted to the head of the occupant from above. The airbag which copes with the aforementioned situation has been proposed ( Japanese Unexamined Patent Application Publication No. 2002-37011).
The generally employed art as disclosed above has a basic structure where the airbag formed by sewing the base fabrics into a bag is stored inside a seat back (or a head rest) of the vehicle seat, and in case of emergency, the pressure fluid from the inflator is supplied to the airbag so as to be inflated and deployed upward of the occupant's head.
In the aforementioned basic structure having the airbag formed of plural bags, the joint portion for distributing the pressure fluid among those bags is required to smoothly distribute the pressure fluid between the bags upon inflation and deployment.